Update the Ubuntu 20.04 LTS runner image

Attempting to run the `ubuntu-20.04` runner image in a GitHub workflow
job generates the following error:
```
This is a scheduled Ubuntu 20.04 retirement. Ubuntu 20.04 LTS runner
will be removed on 2025-04-15. For more details, see
actions/runner-images#11101
```

Author: sgerrand

.github/workflows/ci.yml

@@ -17,57 +17,57 @@ jobs:
         include:
           - elixir: 1.4.x
             otp: 20
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.5.x
             otp: 20
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.6.x
             otp: 20
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.7.x
             otp: 20
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.8.x
             otp: 20
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.9.x
             otp: 20
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.10.x
             otp: 21
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.11.x
             otp: 22
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.11.x
             otp: 23
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.12.x
             otp: 23
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.13.x
             otp: 24
-            os: ubuntu-20.04
+            os: ubuntu-22.04
             gcc: gcc-10
             gpp: g++-10
           - elixir: 1.14.x